The present invention is related to electronic circuits, and more specifically to transient rejecting circuits.
Many electronic circuits are subjected to transients that may adversely affect their intended operation. In lithium ion battery backs, for example, a transient may affect a battery protection circuit. The protection circuit generally attempts to maintain a xe2x80x9cmemoryxe2x80x9d of the state of charging or discharging of the lithium ion battery. When a transient occurs, the memory of the state may be lost.
Additionally, parasitic inductors may be created by the connection of the battery protection circuit to the battery pack and may create large voltage transients when exposed to those currents. The transients can be large enough to cause the effective voltage powering the protection circuit to go to zero, or even go negative for short periods of time, potentially resulting in the memory of the state of charging or discharging of the lithium ion battery to be lost.
Briefly described, the present invention is directed at providing an apparatus and method that maintains previous operational states of a memory circuit during a transient.
According to one aspect of the invention, the apparatus consists of a transient rejecting circuit that during a transient event supplies a signal that maintains the signal at a pin of a circuit.
According to another aspect of the invention, the clear pin of a memory circuit is protected from a loss of signal or an erroneous signal such that, when the induced transient event abates, the memory element is not inadvertently reset.
According to yet another aspect of the invention, the transient rejecting circuit includes a signal transfer circuit and a charge storage circuit. The signal transfer circuit supplies a signal to a pin of a circuit during normal operation, and turns off during transient events. During a transient event, the charge storage circuit supplies the signal to the pin of the circuit.
According to yet another aspect of the invention, the transient rejecting circuit protects a logic pin of the circuit from a transient event. A charge storage circuit charges to the logic signal during normal operation and maintains the logic signal at the pin of the circuit during the transient event.
According to still yet another aspect of the invention, multiple transistors are included in the signal transfer circuit to help ensure that the channel-body diode of the transistors does not drain current from the charge storage circuit. The transistors are connected in series with their body connection connected to the source, helping to ensure that any charging or discharging of the capacitor through the body path is prevented.